The long-term goal of this project is to elucidate the mechanisms by which proteins in the secretory pathway are recognized and destroyed by the ubiquitin-proteasome system (UPS) in a process known as endoplasmic reticulum-associated degradation (ERAD). Substrates committed to this fate are diverse, and include secreted and integral membrane proteins that are unable to fold correctly as a consequence of mutation or inefficient assembly into oligomeric complexes. During the current funding period we have made exceptional progress in achieving our primary aims of establishing a robust and versatile functional genomics platform to map functional substrate-specific sub-networks within the mammalian ERAD system, and have exceeded these aims in developing powerful proteomic tools that have enabled us to compile a preliminary map of the mammalian ERAD interactome. The present application proposes to expand these achievements with the goal of defining the role of chaperones and glycans in luminal ER quality control surveillance and to develop a comprehensive understanding of the composition and functional organization of the ERAD system in mammals. These goals are defined three specific aims. The first specific aim will employ established biochemical, cell biological and biophysical methodology to define the mechanisms by which substrates are committed to ERAD pathway and the role of the molecular chaperone, GRP94, in this process. The second specific aim will conduct a large-scale comprehensive functional genomic screen of the entire UPS in the degradation of a set of topologically diverse ERAD substrates and will validate these components using a battery of informatic and biochemical tools. The third specific aim is to construct a comprehensive map of the mammalian ERAD network by combining in-depth mining of the ERAD proteome with gene silencing to identify network topology, and to overlay this map on the substrate-specific functional network generated in Aim 2. These studies are focused on elucidating the molecular mechanisms by which folding or assembly-defective proteins are destroyed by mammalian cells, and therefore, have direct bearing on human health.